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Mechanisms of resistance

FLT3 D835 mutations confer differential resistance to type II FLT3 inhibitors


Activating mutations in FLT3 occur in ~30% of adult acute myeloid leukemia, primarily consisting of internal tandem duplication (ITD) mutations (~25%) and point mutations in the tyrosine kinase domain (~5%), commonly at the activation loop residue D835. Secondary kinase domain mutations in FLT3-ITD, particularly at the D835 residue are frequently associated with acquired clinical resistance to effective FLT3 tyrosine kinase inhibitors (TKIs). Molecular docking studies have suggested that D835 mutations primarily confer resistance by stabilizing an active Asp-Phe-Gly in (‘DFG-in’) kinase conformation unfavorable to the binding of type II FLT3 TKIs, which target a ‘DFG-out’ inactive conformation. We profiled the activity of active type II FLT3 TKIs against D835 kinase domain mutants that have been clinically detected to date. We found that type II inhibitors (quizartinib, sorafenib, ponatinib and PLX3397) retain activity against specific D835 substitutions. Modeling studies suggest that bulky hydrophobic substitutions (D835Y/V/I/F) at this residue are particularly resistant, whereas mutations that preserve interactions between D835 and S838 are relatively sensitive (D835E/N). All mutants retain sensitivity to the type I inhibitor crenolanib. These results suggest that patients with relatively sensitive D835 mutations should be included in clinical trials of type II FLT3 TKIs.

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This work was supported by grants from the National Cancer Institute (1R01 CA166616-01) (NPS) and the Leukemia and Lymphoma Society (CCS and NPS). CCS is an ASH Faculty Scholar and recipient of a Hellman Family Foundation Early Career Faculty Award. NPS acknowledges the generous support of Arthur Kern, Mark Maymar and the Edward S Ageno family. The authors thank Evan Massi for technical assistance.

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Correspondence to N P Shah.

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NPS has received research funding for the conduct of clinical trials from ARIAD Pharmaceuticals and Ambit Biosciences. NPS has received research funding from Daiichi-Sankyo and Plexxikon Inc. CCS has received research funding for the conduct of clinical trials from Plexxikon Inc. and Astellas Pharma. CCS, KL and A. Stecula designed experiments, performed research, analyzed data and wrote the manuscript. NPS and AS designed experiments, analyzed data and wrote the manuscript.

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Smith, C., Lin, K., Stecula, A. et al. FLT3 D835 mutations confer differential resistance to type II FLT3 inhibitors. Leukemia 29, 2390–2392 (2015).

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